1. Field of the Invention
The present invention relates to a liquid cyrstal display device using a ferroelectric liquid crystal.
2. Description of the Prior Art
As the information related equipment represented by computers has been advanced recently, the role of the display device as an information transmission device is becoming more and more important. A typical conventional display device is a cathode-ray tube, but lately it has been gradually replaced by the liquid crystal device in light of the requirements for downsizing of the appliances and in the reduction of power consumption. There is also a mounting demand for liquid crystal display devices of larger area and larger capacity, of which realization is greatly desired.
As one of the means for realizing such liquid crystal display devices, the liquid crystal device using a ferroelectric liquid crystal has been developed. For the ferrodielectric liquid crystal, usually, chiral smectic liquid crystal is used. Generally, the ferroelectric liquid crystal is designed in a spiral structure in a chiral smectic. However, when implanted in a thin cell, the spiral structure is loosened due to the interface effect. This results in a coexistence of, as shown in FIG. 8 (a), a domain of liquid crystal molecules 18 inclined from a smectic layer normal 17 by an inclination angle +.theta. 19, and a domain inclined in the reverse direction by -.theta. 20. When a voltage is applied to this mixture, as shown in FIG. 8 (b), a domain of aligned spontaneous electrodes, that is, in a state of uniform molecular orientation, is obtained. Or when a voltage is reversely applied, as shown in FIG. 8 (c), a domain in a uniform molecular orientation in the reverse direction to FIG. 8 (b) is obtained. Thus, since the double refraction varies along with application and reverse application of voltage, a liquid crystal display device may be formed by using a polarizer.
In this liquid crystal device, as shown in FIG. 8 (d), even when the electric field is cut off, the molecular orientation, before cutting off the electric field, is maintained by the interface orientation defining power. Thus, a high memory effect may be obtained. In the case of a multiplex drive display of high duty, such a memory effect is very effective. In order to obtain such a memory effect of maintaining the molecular orientation even after cutting off the electric field in both states of inclination angles +.theta. and -.theta., it is required to decrease the difference in the orientation defining power between the upper and lower light-transmissive substrates and reduce the orientation asymmetricity of liquid crystal molecules. Thus, a domain inclined by +.theta. and a domain inclined by -.theta. may coexist.
A typical prior art device is explained with reference to FIG. 7. On the confronting surfaces of a pair of light-transmissive substrates 21, 22, striped transparent electrodes 23, 24 are disposed to form a matrix electrode structure, and orientation films 27, 28 are formed thereon by way of insulation films 25, 26. The gap between the light-transmissive substrates 21, 22 is filled with a ferroelectric liquid crystal 29, and polarizers 30, 31 are disposed on the outer surfaces of the substrates 21, 22. This thereby composes a ferroelectric liquid crystal display device 32.
In such liquid crystal display device, in order to obtain the memory effect in two states of +.theta. and -.theta., the asymmetricity of orientation of liquid crystal molecules is small.
In such conventional liquid crystal display device, voltage is not applied in the region other than the pixel area of the transparent electrode (non-pixel area). Further, since the asymmetricity of the orientation is small, the +.theta. inclined domain and -.theta. inclined domain coexist. Accordingly, as shown in FIG. 9, in the non-pixel area 14 of display screen of the liquid crystal display device, bright regions and dark regions (shaded) coexist. Further, the display screen looks rough, and a uniform clarity is not obtained, and the display quality is lowered.